A. Field of the Invention
The present invention relates to lighting fixtures, and in particular, to lighting fixtures, reflectors, and methods for lighting large areas such as athletic fields from substantially elevated positions.
B. Problems in the Art
Outdoor sports field lighting (e.g. football fields, baseball diamonds, softball fields) are generally lit by suspending a plurality of fixtures on several poles spaced around the fields. A commonly used light fixture for sports lighting is what is called the symmetrical reflector fixture. FIG. 1 illustrates the basic shape of such a fixture.
A symmetrical, bowl shaped reflector 12 is mounted to a mounting structure 14. A lamp 16 generally screws into mounting structure 14. A lens (not shown) is fastened over the front of the reflector 12.
By utilizing a high intensity discharge lamp for lamp 16, the shape of the reflector in combination with reflector 12 can produce a controlled, concentrated, high intensity beam that is useful for sports lighting. A significant advantage to this arrangement is the cost-effectiveness of reflector 12. It can be made of aluminum material, does not require any other supporting structure, and is not subject to rust or corrosion from the outside environment.
The most cost-effective ways to form reflector 12 is to spin it into shape or hydroform it. These are economical ways to make them in large quantities.
First, however, any such forming process cannot be perfect or absolutely repeatable. In other words, because of inherent factors in the manufacturing process, a perfect shape or perfect surface cannot be made during the forming process. Therefore, significant post-forming work is generally required on the interior of the reflector 12. For example, it might be polished, etched, or otherwise worked to assist in creating a desired surface and light output.
It is also to be understood that spun aluminum has on the order of 80% reflectivity. Reflectivity involves a measurement of the amount of light which is reflected from a surface as opposed to being absorbed by the surface. Therefore, 20% or more of the light is absorbed.
There are materials that have higher reflectivity. In fact, some of these materials have reflectivity values on the order of 87% to 97%. Moreover, these materials can be made to be highly specular. Specularity defines what happens to light when it hits the surface. In other words, a highly specular surface is mirror-like. Light will very accurately and uniformly reflect depending on its angle of incidence. A non-specular or highly diffuse surface causes incident light to reflect or spread in all different directions.
Often a controlled amount of spread is desirable to smooth out the light beam. However, it is generally undesirable to have so much spread as to place light outside the desired beam dimension. Controlling the surface on a spun reflector to obtain the desired characteristics discussed above is very difficult and requires a continuous, close control in the spinning and post-forming processes.
Specularity is different than reflectivity. One can have a highly specular surface (polished black marble) with low reflectivity (the black marble absorbs a good portion of the light). Conversely, the high reflectivity material described above not only can be made to be highly reflective (up to 97% reflection with only 3% absorption) but also can be made to be highly specular (mirror like) or diffuse or in between.
It is important to understand that with respect to sports lighting, there are times when you want a surface to be highly specular and times you want it to be diffuse, or in between. In any case though, it is beneficial if reflectivity can be as high as possible because the efficiency of the fixture increases. Light which otherwise would be absorbed and therefore lost from the fixture, can be used for the lighting project.
Therefore, a significant problem in the art is the fact that efficiency is lost by utilizing conventionally manufactured aluminum reflectors. There is room for improvement in efficiency by increasing the total reflectivity of such reflectors.
It is therefore a principal object of a present invention to provide an increased efficiency light fixture, reflector, and method that improves upon the state of the art and solves problems in the state of the art.
Other objects, features, and advantages of the invention include:
1. A reflector that is economically produced yet is highly efficient with respect to total reflectivity. PA1 2. A highly efficient reflector that can have its reflective characteristics varied according to selection and need. PA1 3. A efficient reflector that can be combined with other components to make up a light fixture that is highly efficient and flexible with regard to its light output characteristics and beam characteristics. PA1 4. A reflector that can be used in a light fixture which is durable, flexible, and economical. PA1 5. A light fixture, reflector, and method that is useful in controlling the spread of a light beam and in the shaping of the beam to a configuration which can more closely match the target areas being lighted.
These and other objects, features, and advantages of the present invention will become more apparent with reference to the accompanying specification and claims.